Resistive random access memory (ReRAM) is nonvolatile memory in which a memory element unit has a two-terminal structure including a variable resistance layer interposed between two electrodes. Scaling is considered to be easy because the cell structure is simpler than those of other memory. Therefore, resistive random access memory is drawing attention as a strong candidate for a next-generation large-capacity memory device to replace NAND flash memory which is used widely as large-capacity semiconductor memory devices in products.
Various materials such as transition metal oxides, sulfides, perovskite oxides, semiconductor materials, etc., are being studied as the material of the variable resistance layer of resistive random access memory. Among these, a memory device in which a semiconductor material such as amorphous silicon, etc., is included in the material of the variable resistance layer is expected to be employed due to a high affinity with CMOS processes. However, such a memory device is problematic in that the retention characteristics of the program state are insufficient, etc.; and stable operations cannot be realized.